Method for recovering liquids from gases



PRESSURE: LBS/SQ. m. GA.

y 3 1941. s E. BUC LE'Y 2,242,113

METHOD FO R RECOVERING LIQUIDS FROM GASES Filed March 3 1, 1939 4 Sheets-Sheet 1 LINE OF MAX- -IMUM LlQUiD GROSS LIQUID GAL/MCI GAS new POINT cunv:

TEMPERATURE i F FIG; 2 mm.

BY @M w v %w mom.

GAL. PER mic! May 13, 1941. s. E. BUCKLEY I 2,242,173

METHOD FOR RECOVERING LIQUIDS FROM GASES Fild March 31, 1939 4 Sheets-Sheet 2 GROSS LIQUIDI GAL; PER M.C.F. 7

.GAS

PRESSUREI LBS/SQ. IN; GA.

N NT- OF ORIGINAL GAS GROSS LIQUID 0.4

GAS o.

O 400' 6 I000 7 I400 I600 I800 PRESSURE LBS/SQJNGA.

INVENTOR.

" FIG 4 w jwg y 1941- s. E. BUCKLEY 2,242,173

METHOD FOR RECOVERING LIQUIDS FROM GASES Filed March 51, 939 4 Sheets-Sheet :s

gig

B Y mvmmim ATTORNEY y 1941- s. E; BucKLEY 2,242,173

METHOD FOR RECOVERING LIQUIDS FROM GASES Filed March 51, 1939 r 4 Sheets-Sheet 4 make possibl'e'a substantial recovery Patented May 13, 1941' METHOD FOR RECOVER-1N6: LIQUIDS FROM GASES Stuart E.

Buckley, Houston. Tex, assignor to 7 Standard Oil Development Company, a corporation of Delaware 7 Application March 31, 1939, Serial a. 265,095 c 19 (01. 62-1755) The present invention is directed to a method for recovering normally liquid constituents from gases. -More specifically, this invention is directed to the recovery of gasoline from natural gas and from refinery gases of a composition similar to that of natural gas.

Natural hydrocarbon gas from different sources contains varying amounts of drocarbons which are desirable constituents of gasoline. These gases are usually produced at high pressures ranging upwardly of 1000 pounds per square inch. At these pressures and at ordinary temperatures certain phase lawsoperate which render recovery of'the normally liquid constituents by the conventional scrubbing methods difficult or impractical,- since, under these conditions, although the gas may contain a substantial percentage ofrnormally liquid compo-' nents, the gas as a whole has the characteristics of a 'dry gas. Accordingly, it has been the custom to reduce the gas'pressure considerably, so as to liquid'constituents by scrubbing.

On the other hand, it is frequently desirable to recover the normally dry gas at a high pressure, because this gas is frequently used for repressuring the producing substrata'. Moreover, it is desirable from an economic point of view to conserve the pressure energy of this gas for useful purposes whether or not pressuring. When the gas is to be for repressuring, precompression of it before introduction into the producing substrata for this reason the important factor to be considered is that the cost of compressing a gas to a certain final pressure multiplies rapidly as the initial pressure ingly, it is desirable to recover the normal liquid constituents from the gas with as small a reduction of pressure of the gas as is possible, consistent with an economic recoveryof liquid constituents. That is to say, a balance must struck between the cost of .recompressing the gas and the value of the recovered liquid constituents.

The principal object of mally liquid constituents from gases under high pressure with a reduction in the pressure of gas.

An additional object is a provision of the method of the characterdescribed which can be carried out with simplified equipment and with lower operating and maintenance cost with a mardmum utilization of the energy contained in the gas. r

normal y liquid y it is to be used for reis necessary andthe present invention is the provision of a method for rcovering nor-.

Another object of the present invention is the I densate is utilized to produce refrigeration in the of normally further stabilization of this, liquid condensate.

A further object of the present invention is the provision of a method of the character described in which the normally dry gas which is dissolved in. the liquid condensate recovered is removed from this condensate and subjected to a treatment for the recovery therefrom of condensable constituentswhich it carries off from the condensate.

Further. objects and advantages of the present invention will appear from the following detailed description of the accompanying drawings in which Fig. 1 is a front elevation, partly in section, of one type of apparatus suitable for-the practice of the method of the present invention,

2 is a phase diagram, graphically presenting the phase relations of the liquid and gas phases of a gas mixture of the type to the treatment of which the present invention is applicable.

' Fig. 3 is a graph showing the variation in'gross liquid recovery from such a gas mixture with pressure at various temperatures, a

of the gas decreases. Accord- Fig. 4 is a graph showing the va tion in net gasoline recovery from such'a gas with pressure at various temperatures; I

Fig. 5. is a front elevation in diagrammatic form of an apparatus suitable for carrying out the present inventionin which a gas and adry condensate are delivered;

Fig. 6 is a front elevation of apparatus suitable for carrying out that step of thepresent invention according to which the high pressure of the condensate is utilized in the stabilization of the condensate,

Fig. '7 is a front elevation, partlytin section, of one type of apparatus suitable for recovering dry gas dissolved in the condensateand introducing this gas into the first condensing zone; and

Fig.8 is a front elevation in ditic.

form of a different apparatus suitable for intacting the same results.

In Fig, 1 are applied suitable legends from which the nature of the method of the present invention is evident. Briefly, the method consists in conducting high pressure gas from a deposit a section of an-- from the separator of a refinery plant, which should first be dehydrated by any conventional method or by the method hereinafter described, through a pipe I, a heat exchanger. 2, and an expansion valve 3 into a separator 4, which is maintained at a pressure and temperature within the limits defined hereinafter. The dry gas leaves 7 the separator through a drawofl line 5, which is provided with a valve 6 and leads to a compressor or'to any other piece-of equipment in which the gas is utilized. If it is desired to precool the feed gas, valve 6 is closed and valve 1 ins branch line 8, leading to'the heat exchanger 2, is opened,

whreby the cool gas passes in heat exchange relation with the incoming gas. The dry gas leaves the heat'exchanger through pipe which is connected to the same equipment as line -6. The liquid products recovered in separator l are drawn oil'through line [0 and conducted to a stabilizer, if necessary, or to storage tanks, or to separators and thence-to storage tanks.

. In Fig. 2 is shown a phase diagram or a liquid recovery diagram of a gas mixture of the type,

to the treatment of which the present invention v is directed. In this diagram the various loops A, B, C, D, E and F represent equilibrium curves,

by which is meant a curve showing the.temperature and pressure through which a system containing the designated amount of liquid in gallons per thousand cubic feet of gas can be carried without evaporation or condensation occuring. For example, any point on curve A shows i the temperature and pressure which obtain when the system contains one gallon of liquid for a thousand cubic feet of gas in equilibrium.

The diagram shown in .Fig. 2 represents the phase relation of a mixture of a plurality of-hydrocarbons of various boiling points. For this reason, there are a plurality of envelopes, each designating equilibrium temperatures and pressures for a diflerent liquid content of condensate.

It will be observed that the amount of condensate designated by the envelopes increases ingeneral' pressure between about 500 and 0.2 gallon per 1000 cubic feet will be formed, and that at 1660 pounds per square inch 0.4 gallon will be formed, and that at l300'pounds per square inch 0.6 gallon will be formed, while at 980 pounds per square inch 9. point of maximum condensation or about 0.7 gallon per 1000 cubic feet is reached. Thereafter a decrease in pressure causes vaporization, such that at about 200 pounds per square inch less than'0;4 gallon of condensate will remain.

It will be understood that below line P condensation follows the conventional lawand increases with pressure and decreases with temperature. It should be noted in this connection, with reference to curve B, that the same liquid recovery can be obtained at about 1220 pounds per square inch and --20 F., as can be obtained at about 240 pounds per square inch and -20 F. For practical operation according'to the present invention, liquid recovery is eflected at temperatures between about ,50 and +60 1''. and at a 1,200 pounds per square inch.

It will be understood that the phase diagram shown is not intended to-be a precise picture of the phase relationships of the components of all mixtures treated accordingto the present in- ,vention. In fact, it is not precise with respect to the particular mixture on which it was based. That is to say that every point on the various curves was not determined. Enough points were determined, however, to indicate that the phase diagram takes the general shapesh'own, and this is offered for purposes. of illustration and for a better understanding of the present invention.

' In Fig. 3 is shown, a family of curves which were produced by plotting pressure in pounds per square'inch against gross liquid recovery in gallons'per 1000 cubic feet of gas at various temperatures. It will be observed that in general the amount of gross liquid increases with the decrease in temperature. It can-also be seen that the mount. of recove y Passes through a maximum with increase in pressure and -.then falls =ofl, indicating that the condensation occurring at the point of maximum recovery is retrooutside of the envelope the system is wholly in the liquid phase. A line drawn from 0 to the temperature axis cuts ofl a sector of the diagram to the right of this line in which retrograde action occurs. Along thecurve F is a.point N -.which indicates a-temperature 'at which condensation gradecondensation. In almost every instance; the maximum gross liquid recovery occurred at a pressure above 700 pounds per square inch, al-

' though at some temperatures the amount of recovery' was, very close to maximum at 500 pounds per square inch and fell oif rapidly from this pressure. Again, it will be noted th at 1"..

the amount of recovery fellfofl r pidly after cannotibe effected by an increase or decrease in pressure.- In other words, it designates a tem- That is to sa'y, line P is the lineof maximum peraturebeyond which,any change in pressure cannot affect the condensation; This point is known as cricondentherm. Each of these curves A, B, C, 15 and'Ehas a similar point, and a line P 1 drawn through these points designates the pressureiat which maximum liquid recovery can be had at any given temperature, and vice versa.

liquid production.

Any condensation resulting from a decrease in pressure from apoint above line P is retrograde condensation. For example, assume thata mixture exists at a temperature of about 30 F., as

agas. This point is indicated as point R. It

canbe seen that a reduction in pressure causes condensation, such that at 1840 pounds pressure about 1200 pounds per square inc and that .th'isisalsotrueat20'and401".

. It will be understood thatithese relationships may change for different mhgtlires, such that maximum liquid recovery might be closer to 1200 poimds per square inch. The gen eral relationship holds, however, for mixtures .of this typer In Fig.1 is shown a family. oi curves obtained by plotting net gasoline, R. V. P. 20 pounds per gross constituents dissolved in the liquid. In this case square inch, in gallons per 1000 cubic feet against pressure in pounds per square inch, the original gas containing about 0.52 gallon per 1000 cubic feet. It will be understood that the redson-for the lower values in this family of curves, is that the condensate represented in the family of curves in Fig. 3' includes normally gaseous it can be seen that maximum net liquid recovery occurs more nearly at 500 pounds per square inch than at 700 pounds per square inch, and

V r 7 2,242,173 that beyond 1200 pounds per square inch the recovery falls ofi even more sharply than was the case with gross linuid recovery. Beginning at about 40'F., 700 pounds per square inch appears to be the minimum preferred pressure for increase in temperature. Y

Referring to Fig. 5, parts corresponding to those shown in Fig. I bear the same numerals. The apparatus shown in this figure difiers from that shown in Fig. 1 by including a line for the circulation to the heat exchanger and the separator of a liquid having a greater aflinity for water than oil. This liquid should be one which remains liquid at temperatures as low as those at which itis desired to operate and will boil at least as high as butane. In general, this liquid is mixed with the wet gas before the latter is expanded into the separator, whereby the water in the wet gas is taken up by the liquid which settles out in the separator with the oil,

with which it, or at least its water solution, must be immiscible, in order to be operative. Suitable liquids for use in this connection are the various glycols, such as ethylene glycol, glycerol, concentrated inorganic salt solutions, and the like. Referring to the drawings, line H is provided at the bottom'of the separator 4 for drawing off the .water absorbent and conducting it back tothe feed inlet l, preferably after compressing it by pump l2 to a pressure such that it will enter desired constituents at the pressure employed.

The chief undesired constituents are propane andlower hydrocarbons, and a certain percentage of the butane which must be removed in order to reduce ,the vapor pressure of the gasoline to the desired amount. Line ID from tower 4 of Fig, 1 passes into the top of tower l3 in which i it is formed into a coil l1, and then back out to a heat exchanger II! where it is passed in heat and expansion valve 3 and with the zone maintained under conditions heretofore proposed the condensate collects at the bottom thereof, while dry gas passes off at the top through line 5. The

condensate is withdrawn through line 23 and 'coil 25, which is supplied with steam at a suitable temperature to drive off normally gaseous constituents of the condensate at the pressure maintained in the system. The gases so driven off are withdrawn through the lower section through line 25 andpassed in heat exchange re-v lation to the liquid withdrawn from the upper zone, and arethen discharged into the upper end of the upper zone to join the dry gas leaving the system through line 5. The condensate with a reduced content of normally gaseous constituents, such as methane and ethane, is withdrawn from the lower section through line 21.

In the system shown in Fig. 8 the object is to recover dry gas which has been dissolved in the condensate and at the same time stabilize the condensate without the loss in the dry gas of constituents, such as propane and butane, which may be desired for some other purpose. In this "system the rich gas is introduced through line 28 into a heat exchanger 29 where it gives up heat ,to the condensate initially produced, and is then passed through a second heat exchanger 30 where it gives up heat to the dry gas initially produced, and then passes through expansion valve 3| into the separator 34. The condensate is withdrawn from the separator through line and passed to heat exchanger 29, while dry gas is withdrawn from the separator through line 36 and passed through heat exchanger 39, and then to a second heat exchanger 37 hereinafta' referred to. Separator 34 is provided at'its upper end with'a cooling coil 38 which need not be" used if sufiicient temperature reduction can be secured by expansion of the wet gas.

The condensate leaving tower 34 contains some dry gas dissolved therein, and this condensate is heated up in heat exchanger 29 and then passes through line 52 to a flash drum 39 from the upper end of which the dry gas passes off through exchange relation to the stabilized gasoline which has been heated up by the steam coil carried in line I5. The stabilized condensate is withdrawn from the heat exchanger by line l9. Prior to its entry into the tower the unstable condensate is passed through an expansion valve 20 which causes expansion of this condensate in coil H with consequent coollng. By this expedient the pressure of the condensate is utilized to produce reflux in the top of the stabilizer by reducing the temperature of coil H to any desired point, and easily to the temperature required to maintain the composition of the overhead so that it contains nothing higher than butane. g

In Fig. '7 is shown a tower which may be substituted for separator 4 in Fig. 1, and which enables the operator to recover thedry gas which has been dissolved in the condensate fromthe condensate without a loss of its pressure. The tower shown in Fig. '7 is indicated'by numeral 2| and is provided with a partition 22 intermediate its ends dividing it into two zones. The wet gas is introduced into the upper zone through line r top with a cooling coil 45.

line 40. This dry gas inevitably carries ofiE some desirableconstituents with it, so it is added to the feed stock atthe low pressure side of expansion valve 3|. The remainder of the condensate is withdrawn from drum 39 through line 4| and is discharged through a heat exchanger 42 into' a stabilization drum,43. Stabilizer 43 is provided at its bottom with a heating coil 44 and at its The overhead from the stabilizer passes off through line 46 to. heat exchanger 31 where it is cooled by the dry gas withdrawn from separator 34, and is then combined with the fresh feed at the low pressure side of expansion valve 3|. 1

, Stabilized liquid is. withdrawn from the bottom of stabilizer 43 through line 41, and is conducted to a heat exchanger 42, where it'impar-ts its heatto the incoming condensate. Line 4| is I provided with a bypass 48 containing a pump 49,

while line 46 is provided with a bypass 50 containing a compressor. 5|. Since it is desirable necessary either to compress the condensate from flash drum 39 and to operate the-stabilizer 43 at this pressure, or to compress the overhead from the stabilizer. The former is generally the more economical procedure.

In order to impart flexibility to the system, line 52 is provided with a bypass 53 in which is a pump 54, and line 40 is Provided with a bypas 55 in which is a compressor 56. Thus separator 39 may be'operated at fairly low pressures. and the gases resulting therefrom are compressed in compressor 56, and the liquids pumped by pump 48 into stabilizer 43. Alternatively, stabilizer 43 can also be operated at low pressure and .the gases resulting therefrom compressed by compressor 5i. Or by the use of pump 54, the separator 39 may be operated at relatively high pressure and the stabilizer 43 at relativelylo'w pressure.

can be seen, the system illustrated in Fig. 8 utilizes to thefullest extent the energy contained in the various components of the initial mixture,

and yields a stabilized gasoline and a dry as at a.

high pressure which may be used-for repressuring producing formations or for any other purpose where high pressure gas is desired. It .will' be understood that the drying'arrangement shown in Fig. 5 is applicable to the apparatus shown in Fig. 8 as well as to the apparatus shown in the Likewise, the condensate line in, Fig. 8, instead of going to the first heat exother figures.

changer, can go tothe stabilizing tower as shown in P18. 6

From the'above description, it will be apparent that the present invention relates to the recovery of condensable constituents from high pressure 'vers'ely, the gas may' be cooled wholly by expansion without the aid of heat exchangers or extraneous refrigeration.

tion having been thus described and illustrated,

what is claimed as new and useful and is desired to be secured by Letters Patent is:

-1. The method of recovering desirable liquefiable constituents from natural gas which is initially at a higlnpressure within the retrograde condensation r e of said constituents which comprises, cool? pressure substantially only within the retrograde condensation range of said constituents at the reduced temperature, and separating the resulting condensed constituents from uncondensed gas.

2. The method of recovering desirable lique-' fiable constituents from natural gas which is ini tially at a high ipressure within the retrograde condensation range of said constituents which comprises, cooling said gas sufiiciently to congases containing them, the recovery to be effected at a pressure of at least 500 pounds per square inch. As has been shown, the operation is pref: erably conducted at a pressure of at least 700 pounds per square inch and may be conducted at pressures as high as 1200 pounds per square inch, provided the initial wet gas is available at pressures substantially in excess of 1200 pounds per square inch, such as 20061 pounds per squareinch which is quite common in many fields. The separator maybe maintained at any convenient temperature of between about .and R, the lower temperatures in this case being rather cheaply attained,'when the wet gas is at a sufficiently high pressure, by expansion of thegas tothe separation pressure with suitable heat exchange.

1n the" appended drawings apparatus has been shown in which the high pressure gas is expanded in the separator so that the desired temperature in the separator can be attained, -In some cases the initial gas is not at sufficiently high pressure to produce the desired low temperature merely "by expansion to the operating pressure. -In this case it'will be evident that the temperature of the separator may be maintained by extraneous refrigeration, such as by the employment of coolingcoilssuchasshowninFig.8.

The method, as practiced in the various types 'of apparatus shown in the drawings, consists in taking a gas, containing normallyliquid constituents, above the desired separation temperature, preferably dehydrating the g s. 0ling thegas initially to a lower temperature and then releasing the, pressure on the gas to bring it to the desired separation pressure and temperature. It

2 will be understood that no particularorder of steps'is necessary in arriving'at the separation conditions. -Th ef important point-is the arrival at-the separation conditions and the maintenance of these conditions. Thus, for example, the gas f y can initially be expanded to the separation pressure and then cooled, if further cooling is nee essary, to the separation temperature. Con? dense said-constituents while the gas is maintained under said high pressure, thereafter reducing .said high pressure substantially only within the retrograde condensation range of said constituents at the reduced temperature, and separe-ting the resulting condensed constituents from uncondensed gas.

3. The method of recovering desirable fiable constituents from natural gas which'is initially at a high pressure within the-retrograde condensation range of said constituents which comprises, precooling said gas while under said high pressure to a temperature below its initial temperaturebut above the final desired temperature for condensation of'said constituents, then reducing said high pressure substantially only within the retrograde condensation range of said constituents at said final temperature and thereby to further cool said gas to said final temperature, and separating the resulting condensed consti-tuents from uncondensed gas.

4. The method of recovering desirable liquefiable constituents from natural gas which is initially at a high pressure within the retrograde condensation range of said constituents which comprises, cooling said gas below its initial tempe'rature while said gas is maintained under said" high pressure, thereafter reducing said high pressure sufiiciently only to produce retrograde condensation of said constituents at the reduced' temperature, separating the resulting condensed constituents from uncondensed gas, and utilizing the refrigeration effect produced in the gas by the reduction in pressure to accomplish the I aforesaid cooling. l

recovering desirable lique- 5. The method of fiable constituents from 'natural. 'gas which is initially at a pressure above 700 pounds per square inch which comprises, cooling said gas to a suitable condensation temperature for said constituents, reducing the initial pressure of the gas substantially only within the retrograde condensation range of said constituents at said condensation temperature but not below 700 pounds per said gas sufliciently to condense said cons tuents while reducing said high liquesquare inch, and separating the resulting conand separating the resulting condensed constitudensed constituents from uncondensed gas.

6. The method of recovering desirable liquefiable constituents from natural gas which is initially at a pressure above 700 pounds per square inch which comprises, cooling said gas while under said pressure to a. temperature below its initial temperature but above the =final desired temperature, then reducing said initial pressure substantially only within the retrograde condensation range of said constituents and to thereby further cool said gas to said final temperature, and separating the resulting condensed constituents from uncondensed gas.

7. The method of recovering desirable -liqueents from uncondensed gas.

12. The method of recovering desirable liquefiable, constituents from natural gas which is initially at a high pressure within the retrograde condensation range of said constituents which comprises, cooling said gas sufliciently to condense said constituents while the gas is main: tained under said high pressure, thereafter reducing said high pressure substantially only within the retrograde condensation range of said constituents at the reduced temperature, separating the resulting condensed constituentsfrom fiable constituents from gas which is initially at a a pressure above 700 pounds per square inch which comprises, subjecting said gas to multistage cooling to condense said constituents while reducing the initial pressure of said gas substantially only within the retrograde condensation range of the desired constituents at the final temperature, separating condensed constituents from uncondensed gas, and cooling the gas in at least one of the cooling stages by the refrigeration effect produced by the reduction in pressure of- 'the gas.

8. The method of recovering gasoline constituents from natural gas which is initially at a pressure above 700'pounds per square inch which comprises, subjecting saidgas to multi-stage cooling to condense said constituents while reducingthe initial pressure of the gas substantially only within the retrograde condensation range of the desired constituents at the final temperature but not below 700 pounds per square inch, separating condensed constituents from uncondensed gas, and cooling the gas in at least one of the cooling stages bythe refrigeration effect produced by the reduction in pressure of the gas.

9. The method or recovering desirable liquefiable constituents from gas which is initially at a high pressure within the retrograde condensation range of said constituents which comprises, cooling said gas in a series of cooling stages of progressively decreasing temperature to a final temperature suitable to condense said constituents, reducing said pressure only in the reducing theim'tial pressure of the gas substantially only within-the retrograde condensation range of said constituents, thereafter cooling said gas to condense saidmonstituents, and separatin the resulting condensed constituents from uncondensed gas. j

11. The method of recovering desirable liquefiable constituents from gas which is initially at a pressure above 700 pounds per square inch which comprises, reducing the initial pressure of the gas substantially only within the retrograde condensation range of said constituents but not below 700 pounds per square inch, thereaftercooling said gas to condense said constituents,

sulting condensed constituents irom uncondensed 14 The method of recovering desirable lique fiable constituents from gas which is initially at a pressure above the retrograde condensationrange of said constituents which comprises, cooling said gas to a suitable condensation temperature for said constituents, reducing the intial pressure of the gas to a pressure within the retrograde condensation range of said constituents at the temperature of operation, and separating the resulting condensed constituents from uncondensed gas.

15. The method of recovering desirable liquee fiable constituents from gas which is initially at a pressure above 500 lbs/sq. in. which comprises,

cooling said gas by 'heat exchange with a cooling medium to a suitable condensation temperature for said constituents, reducing the initial pres sure of-the gas to a pressure within the retrograde condensation range of said constituents at the temperature of operation, but not below about 500 lbs/sq. in., and separating the result ing condensed constituents from uncondensed gas.

16. The method fiable constituents from gas which is initially at a pressure of a considerably above about 500 lbs/sq. in. which comprises, cooling said gas to a suitable condensation temperature within the range of +60 to -50 F., reducing the initial pressure of the gas to a pressure within the retrograde condensation range of said constituents at f the selected temperature, but not below 500 lbs/sq. in., and separating theresulting condensed constituents from uncondensed gas.

17. The method of recovering desirable lique-' fiable constituents from gas which is initially at a pressure substantially above about 500 lbs/sq.

in., which comprises'cooling said gas to a suitable condensation temperature not in excess of about 20 F., reducing the initial pressure of the gas to a pressure within the retrograde condensation range ofjsaid constituents at the temperature of operation, but not below 500 lbs/sq. in., and

, separating the resulting condensedconstituents from the uncondensed gas. r n 18. Themethod of recovering desirable liquefiable constituents fromgas which is initially at of recoverin desirable liquea pressure substantially above about 1200 lbs/sq.

in. which comprises, cooling said gas to a temperature within the range between +60 and -50 F., reducing the initial pressure 01' the gas to a pressure below 1200 lbs./sq. in. but not below 500 lbsL/sq. in., and separating the resulting condensed constituents from uncondensed gas.

19. The method of recovering desirable liqueflable constituents from gas which is initially at a pressure above the retrograde condensation 10 range of said constituents which comprises, cooling said gas to a suitable condensation temperature for said constituents within the range of +60 to --50'' It, reducing the initial pressure of the gas to a pressure within the retrograde condensstion range 01' said constituents at the temperature of operation, and separating the resulting condensed constituents irom uncondensed STUART n 'nUcKm'Y. 

